High Spatial Resolution Thermal Mapping of Volatile Switching in NbO-Based Memristor Using In Situ Scanning Thermal Microscopy

Temperature mapping by in situ thermoreflectance thermal imaging (TRTI) or midwave infrared spectroscopy has played an important role in understanding the origins of threshold switching and the effect of insulator-metal transitions in oxide-based memrsitive devices. In this study, we use scanning thermal microscopy (SThM) as an alternative thermal mapping technique that offers high spatial resolution imaging (∼100 nm) and is independent of material. Specifically, SThM is used to map the temperature distribution in NbO-based cross-bar and nanovia devices with Pt top electrodes. The measurements on cross-bar devices reproduce the current redistribution and confinement processes previously observed by TRTI but without the need to coat the electrodes with a material of high thermo-reflectance coefficient (e.g., Au), while those on the nanovia devices highlight the spatial resolution of the technique. The measured temperature distributions are compared with those obtained from physics-based finite-element simulations and suggest that thermal boundary resistance plays an important role in heat transfer between the active device volume and the top electrode.